PROVIDENCE - From a cramped office in the middle of the smallest state in the nation, Christopher Plante is determined to prove that Rhode Island has not been cornered by the advance of same-sex marriage across the rest of New England.

"When I look at a real map of the United States, we're actually not alone here," said Plante, executive director of the Rhode Island chapter of the National Organization for Marriage, which opposes same-sex unions. "This is not the United States of New England."

But supporters and even some opponents expect that Rhode Island will legalize same-sex marriage, although they say that legalization is two or three years away.

Massachusetts and Connecticut legalized same-sex marriage as a result of judicial decisions in 2003 and 2008, while Vermont, Maine, and New Hampshire followed this spring by legislative action.

The slower pace in Rhode Island, where the state Senate voted last week to allow same-sex partners to make funeral arrangements, has frustrated some local activists, many of whom rallied outside the State House in Providence last weekend to call for immediate equality.

But others say that legalization by 2012, a goal advocates set last year for securing same-sex marriage in all New England states, would put Rhode Island at the front of the pack nationally. In the rest of the country, only Iowa allows same-sex couples to marry.

"They still have a chance to be part of the vanguard," said attorney Karen L. Loewy, the Rhode Island point person for GLAD, which won the lawsuits in Massachusetts and Connecticut that legalized same-sex marriage in those states. "Rhode Island is well on its way."

Founded in 1636 by Roger Williams as a "lively experiment" in religious freedom and tolerance, Rhode Island is the most Catholic state in the nation. The influence of the church, as well as the inclinations of a large blue-collar voting bloc, has led the state to advance progressive policies in areas such as children's healthcare, but to tread conservatively on matters such as abortion and gay rights, said state Senator Rhoda E. Perry, a Democrat from Providence's East Side.

Perry, whose liberal-leaning district includes Brown University, has sponsored same-sex marriage legislation for several years, so far unsuccessfully. Support has grown, but the votes are not yet there in the Senate, where the change also lacks the support of the Democratic Senate president.

In the House, lawmakers have filed same-sex marriage legislation almost annually since 1997. No longer dismissed as a fringe bill, the legislation attracted nearly half of the 75 members as cosponsors this year, though it is opposed by the Democratic speaker. The bill remains in committee for further study.

But a floor vote would be futile, advocates acknowledge, because Governor Donald L. Carcieri, a Republican, has vowed to veto any same-sex marriage bill. Carcieri, however, is barred by law from seeking a third term, and many Rhode Island political observers expect the 2010 election to bring a successor who would not veto such legislation.

Meanwhile, support for same-sex marriage appears to be growing among the public.

Late last month, a Brown University poll found that 60 percent of registered voters surveyed support legalizing same-sex marriage, with 31 percent opposed. Plante and other opponents were skeptical, given that a poll conducted last summer by Marriage Equality Rhode Island, which advocates legalization of same-sex marriage, found a much narrower gap: 49 percent in favor and 37 percent opposed.

But the director of Brown's Taubman Center for Public Policy, which conducted the poll of 593 voters statewide, said popular opinion might be shifting quickly as Rhode Islanders watch neighboring states legalize same-sex marriage.

Mayor David N. Cicilline of Providence said he thinks the 2012 goal is attainable, adding that grass-roots outreach and a growing acceptance of gay and lesbian people have led more people to view the issue as a matter of equality.

"I think we are changing people's hearts and minds," said Cicilline, who is gay. "I don't think it's unusual for the public to be ahead of elected officials. That often happens on issues of civil rights and nondiscrimination."

Before Plante hung out a shingle for the National Organization for Marriage this spring, the Roman Catholic Diocese of Providence led the campaign against gay marriage.

But even the bishop has acknowledged that his side has lost ground. In April, he penned a call-to-arms editorial headlined "Rhode Island, Most Catholic State, Welcomes Gay Marriage."

"That's a headline we haven't seen yet, dear readers, but probably will in the next couple of years," Bishop Thomas J. Tobin wrote in The Rhode Island Catholic, contrasting the "relentless" advance of same-sex marriage with what he called "abysmal apathy" of most of the state's Catholics.

Plante said he thinks same-sex marriage can be forestalled.

"We're going to fight for our home," he said, vowing to mount vigorous bids to remind office-seekers that the older residents who turn out on Election Day disproportionately oppose same-sex marriage.

Meanwhile, the former elementary school teacher said he plans to reach out to young people to dissuade them from thinking about same-sex marriage in terms of equality.

"Civil rights is a nice code word to get people to be afraid, afraid of being unfair," Plante said. "This is about a social experiment to redefine marriage and radically change the American family and the American community."

Activists on the other side are trying to win neighbors one at a time. "The older generation, they don't know they know gay people," said Representative Frank G. Ferri of Warwick, who co-founded Marriage Equality Rhode Island and stepped down as executive director to seek office.

Ferri, who married his partner of 25 years in Canada in 2006, owns a bowling alley in Johnston, where he receives good-luck wishes from the retirees who frequent his lanes.

"They tell me that it's going to happen," said Ferri, who also thinks that legalization is likely by 2012, "not that we want to wait that long."